Use of control circuitry for generating signals necessary to operate various devices or control elements in a machine is generally known. For example, xerographic copier/duplicator machines based on Chester Carlson's invention in the electrostatographic copying principles usually includes control means for implementing various steps involved in making xerographic copies; for example, means for charging a photosensitive insulating layer, imagewise exposing the layer, developing the image with toner, transferring the image on a sheet of paper, removing the sheet, heat fusing the transferred image on the sheet, and cleaning the layer for subsequent use, etc. The means for achieving these steps include certain controlled elements for implementing the various xerographic processing steps; for example, means responsive to a signal for actuating the main drive motor of the machine, common generating means for charging the photosensitive insulating layer or transferring the image on the layer onto the transfer sheet or copy paper, magnetic brush developer means, means for cleaning the layer, scanner carriage and optical scanning means for projecting the image of the original onto the photosensitive insulating layer, jam detection means, etc. The machine is usually provided with a suitable control logic circuitry for generating appropriate signals required to actuate or energize the various controlled elements in a timed sequence so that the xerographic steps are properly implemented.
Heretofore, generally the copier/duplicator was designed to operate in a single mode in making copies of the original. For example, the typical machine was designed so that its optical scanning arrangement moved past an original in a stationary position, or in the alternative, the scanning arrangement was held in a fixed or a stationary position while the document original was fed past the scanning arrangement in making copies up to a certain size. Such machines had an inherent limitation, in that, for example, they were capable of making copies only up to certain given size, such as legal size paper (81/2 .times. 14 inches), but not capable of making copies on a sheet which is larger than this given size.
More recently, however, there has developed a copier/duplicator machine which is capable of operating in more than one mode of operation for making copies of different sizes. An example of such a machine is described in detail in the copending case, U.S. application Ser. No. 284,687, filed on Aug. 29, 1972, now abandoned and replaced by continuation application Ser. No. 367,996, filed on June 7, 1973, now U.S. Pat. No. 3,900,258, both applications being assigned to the same assignee as the present invention. As described in the application, the machine is designed so that in a first or base mode of operation a moving optical scanning means is used in scanning a stationary original and in a second or LDC mode of operation the scanning arrangement is stationary and the document original is moved past a scanning station by a document feeding means. The machine is designed so that, in the base mode, it can make copies in normal letter size, (e.g., 81/2 .times. 11 inches) and up to legal size (e.g., 81/2 .times. 14 inches) and in the LDC mode or Large Document Copy mode, copies up to 14 .times. 18 inches can be made.